The present invention relates to detecting the accumulation of soot or carbon particles in diesel engine lubricant. It has been found that recent reductions in mandated limits for vehicle engine exhaust emissions have required fitting diesel engines for use with exhaust gas recirculation (EGR) valves to dilute the fuel-air charge ratio. This has resulted in changes in combustion chemistry and an increase in the rate of build-up of soot blowing past the engine piston rings and contaminating the engine lubricant oil.
The presence of soot above a threshold concentration has been found to render the engine lubricant unable to effectively perform its function and engine damage becomes imminent.
Heretofore, available means for determining soot concentration in engine lubricant were laboratory techniques which required taking a sample of the engine oil to a laboratory for analysis and performing Thermo Gravimetric Analysis or using optical techniques such as Fourier Transform Infrared Spectroscopy to determine the amount of soot present in the lubricant fluid. This has proven to be prohibitively costly and time consuming and thus virtually unworkable when it is necessary to monitor the oil condition of a diesel engine during operation in service.
It is known to use Impedance Spectroscopy in monitoring the condition of engine lubricant fluid during real time operation in engines such as shown and described in U.S. Pat. Nos. 6,278,281, 6,377,052 and 6,380,746. The aforesaid technique utilizes differential Impedance Spectroscopy to detect depletion of the lubricant constituents added by the manufacturer during blending. However the impedance spectroscopy algorithms set forth in the aforesaid patents have been found unable to monitor soot in diesel engine lubricant.
Thus, it has been desired to find a way or means of monitoring diesel engine lubricant during real time operation of the engine and in particular to monitor the concentration of soot.